<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>流程控制</title>
</head>
<body>
<script>
  let username='';
  // if (!username){
  //   alert('用户名不能为空');
  // }else {
  //   alert('欢迎'+username+'回归！');
  // }
  //选择分支
  let gender = 1;
  switch (gender){
    case 1:
      console.log('男');
      break;
    case 2:
      console.log('女');
      break;
    default:
      console.log('未知');
  }
  //循环结构
  let names=['张三','李四','王五','赵六','钱七'];
  for (var i = 0 ;i<=names.length;i++){
    console.log(names[i]);
  }
  console.log('循环结束'+i)
  //增强for循环
  //let n表示当前遍历到的元素
  for (let n of names){
    console.log(n);
  }
</script>

</body>
</html>